Even in their spare time, astronauts onboard the
ISS are discovering new and surprising things about nature.

Like the other members of the International Space Station's
3-person crew, he's busy most of the week doing research and
building the ISS, where he's been living for the past three months.
"Saturday is when we have a bit of free time," Pettit
says. Some of the crew read books, play musical instruments or
watch movies. "I prefer to do 'Saturday Morning Science'--fun
experiments of my own design."

Right: International Space Station science officer Don
Pettit. Don is a member of ISS Expedition 6. He's been in space
since Nov. 2002. You can read more about his experiences here.

A few Saturdays ago, he had his heart set on bubbles.
"We have a copy of C. V. Boys' book Soap Bubbles
here on the ISS. It was published in 1911 and it's still a wonderful
treatise on thin films. Every space station should have a copy,"
he laughs. "I wanted to see what thin films and bubbles
might do in zero-g and felt it was a topic ripe for discovery."

Pettit prepared a solution of water, soap, and glycerin, and
fashioned a bubble-wand from thin wire--a loop that could be
re-sized from 3.5 cm (about 1.5 inches) to more than 15 cm (6
inches) in diameter. The experiment was ready. "But first,"
recalls Petit, "I decided to try a 'dry run' with water
only, no soap."

He inserted the wand into a zero-g beaker and pulled
it out again. "To my amazement," he says, "when
the 2-inch loop was withdrawn, a thin film of water clung tenaciously
to the loop. I've never before witnessed such a large-scale film
of water."

Left: Pettit shakes a remarkably sturdy film
of water onboard the ISS. See the full-length movie: Reel
1, Reel 2.

To fully appreciate Pettit's discovery, just try the experiment
in your own kitchen (on Earth). Fill a bowl with drinking water
and fashion an adjustable loop of wire. No matter how hard you
try, it's impossible to make water stretch across a loop wider
than about 1 cm (0.4 inches). Any film you do make, furthermore,
will be fragile. A gentle bump or breath of air will cause it
to burst.

Pettit's films, on the other hand, were 5 to 11 cm (2 to 4
inches) in diameter and remarkably sturdy. He could shake them
vigorously, blow on them ... even paint on them. "They were
like little sheets of rubber," he marveled. "They could
withstand all sorts of mechanical torture."

Why are space films so tough? To understand the difference
between Earth films and space films, it's helpful to understand
surface tension.

Surface tension is what allows water bugs to scamper across
ponds without sinking. It's a stretchy "skin" across
any wet surface that resists penetration. This skin exists because
water molecules are electrically charged. The positive end of
one molecule is drawn to the negative end of another: water literally
clings to itself!

Right: Cohesive forces between water molecules are greatest
near the surface. Click on the image to find
out why.

The
electrical attraction between water molecules, and thus the surface
tension of water, is the same on Earth and in space. There's
no difference.

What is different is the competition between surface
tension and gravity.

Let's say you're on Earth and you have a thin film of water
held parallel to the ground. The pull of gravity causes the film
to sag in the middle. Water drains downward from the edge of
the loop; a little pool forms. The film sags more. The pool gets
bigger and bigger until its weight rips the film apart.

If you're in Earth orbit, however, the film would be in free
fall--weightless. The film doesn't sag. The central pool never
forms. Surface tension therefore wins the competition with gravity,
and the result is a sturdy long-lasting membrane. "Some
of our films lasted longer than 12 hours," notes Pettit.

What do you do with a membrane of water? The entertainment
value alone is impressive.

Pettit spent some time simply making the wand bigger and smaller.
"Oscillating the loop with a period of about 2 seconds distorted
the film with remarkable patterns like you might see in a rubber
membrane driven by a sound oscillator. The back-and-forth displacement
at the center was several centimeters."

Next, Pettit injected some tiny mica flakes
into the film. This allowed him to observe otherwise-hidden flows
and swirls. "I blew on the film using my own breath,"
says Pettit, and fascinating patterns emerged--some that looked
like spiral galaxies. "These tracer particle patterns lasted
for well over four hours."

Then it was time to paint. On one film, Pettit deposited four
drops of food coloring: red, blue, green and yellow. Using a
syringe with a thin tip (a canella), he shot a stream of air
across the watery canvas, pushing the colors to and fro. One
of his paintings looked like an eagle, others like abstract art.

"I wonder what someone like Matisse could do with this
ephemeral medium?" wonders Pettit. "Eventually, all
the colors blended together yielding a rather dull looking green.
I think we've discovered the true color of the Universe!"
he joked.

Seriously, though, these films highlight the value of space
for fundamental research in fluid physics. Fluid flows on Earth
are complicated by gravity-driven convection and 3D motions.
A 2D film of weightless water is a splendid research tool that
could yield data of value to many industries on Earth.

Right:
A new form of art by space station science officer Don Pettit.

Meanwhile, Pettit hasn't forgotten his original experiment:
"We never got to the soap solution because we were diverted
by plain water. We'll do soap bubbles on another Saturday,"
he says.

What will they reveal? No one knows.

"Observations of nature, no matter how seemingly arcane,
are like peeling off one more layer from the great onion of knowledge,
tickling your imagination with what you have found but always
revealing yet another tantalizing layer underneath," says
Pettit.

"I hope we never get to the core."

Editor's note: Science@NASA will publish a series
of stories about Don Pettit's Saturday Morning Science
activities in the weeks ahead. Stay tuned! And while Don's experiments
are done for fun, motivated by his own curiosity, there is also
serious scientific research underway involving fluids and foams
in microgravity. We'll report on those experiments in an upcoming
story.

The Science and Technology Directorate at NASA's
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